The present invention relates generally to an improved system for handling thermoplastic film products such as plastic bags or the like, and more particularly to an improved system for accommodating stacking or delivery of these devices from a converting machine or apparatus. Generally, thermoplastic film converting machines such as bag making machines employ a constant speed conveyor to receive products from the final working station of the converting machine, and the system of the present invention provides means for forming a stable air foil of the film product while controllably attenuating or retarding the rate of speed of these products as they are driven from the terminal end of the conveyor, whereupon they are normally stopped against a stacking gate.
The principal purpose of the stacking wheels or "corrugating wheels" as they are sometimes referred to, in an apparatus fabricating thermoplastic film products is to form the product into a more stable air foil, and thus permit high speed delivery of the product from the converting machine to a product receiving station such as a stacking gate. Normally, the stacking wheels or corrugating wheels provide a generally sinusoidal transverse profile to the film product as it moves therethrough, thus achieving a corrugated effect in the product, with the corrugations generally being along an axis parallel with the traveling axis of the web. In order to reduce the speed at which individual film products approach a stacking gate or barrier member, a rotating blade or paddle is frequently interposed along the path of travel, and the rotating blade strikes the film product and frictionally engages the product against a flat planar surface. Such activity, of course, destroys the corrugated effect in the product, and tends to reduce its effectiveness as an air foil.
In the fabrication of thermoplastic film products, such as bags or the like, the products are normally fabricated in the converting equipment on a continuous line basis wherein the individual operations conducted on the plastic film are carried out at one or more working stations. Thus, the converting machinery will normally be provided with a working surface, along with means for receiving a supply web of thermoplastic film to be moved therethrough, the movement normally being in the web direction of the machinery. After preparation of the products within the converting equipment, the individual thermoplastic film articles or products are transferred to a constant speed conveyor and from the conveyor, ultimately on to a product receiving area, normally a stacking gate. At the article receiving station, such as the stacking gate, the products are normally stacked in superimposed relationship, one upon another, until a specific predetermined number of articles are received.
The rate of production is normally limited by the rate of speed at which the material can be conveniently removed from the individual working stations. Thus, while the web of material may be moved at a reasonably controllable rate of speed, the limiting factor for production is normally determined by the rate at which the individual articles may be removed from the working stations. While a high speed conveyor is usable for removing the individual completed articles from the final working stations, ultimately these individual articles must be transferred on to a receiving station such as a stacking gate or stacking table. Inasmuch as these thermoplastic film products or articles have significant length and width dimensions, when they are moved at high rates of speed, these articles are subject to interference from air currents or ambient air, and thereby tend to lose whatever rigidity and stability that may be induced when undergoing transfer as an air foil from a conveyor to the product receiving station. Curling, folding, or other anomolies may be introduced into the article when ultimately transferred from the conveyor to the product receiving station. The present invention makes it possible to transfer the completed film products from the conveyor on to the stacking table at a high rate of speed and under stable and controllable conditions and as an air foil or projectile.
In the fabrication of thermoplastic film products from a continuous web, the individual finished articles are necessarily separated and transmitted in spaced relationship from the final working station. This is necessary in order to eliminate any danger of having fused portions of mutually adjacent articles becoming bonded to mutually adjacent distinct articles. Therefore, the highest rate of lineal speed in the overall converting machinery is normally found in the conveyor leading from the final treating station, this conveyor providing spacing between individual and sequential film products. Speeds in excess of 200 lineal feet per minute are common in conventional bag-making equipment.
While various techniques have been employed in order to increase the longitudinal rigidity and stability of film products as they leave or are discharged from the conveyor and enter the stacking area, the primary technique utilized is to pass the individual articles through corrugating wheels or the like wherein the longitudinally extending transversely corrugated configuration is introduced to the article. Thus, the individual articles may be transferred as air foils or projectiles on to the stacking gate. The stability of the product so transferred therefore depends on its ability to retain its corrugated configuration, and thus means for limiting the tendency of the product to revert to the planar configuration will enhance the transferability of the products. As indicated above, the present use of blades or paddles against the surface of the corrugated film product tends to disrupt the stabilizing configuration.